Autism is a complex developmental disability that interferes with normal development of the brain in the areas of social interaction and communication skills. Typically, autistic children and adults have difficulties with verbal and non-verbal communication, social interactions, and leisure or play activities.
Autism generally is characterized as one of five disorders coming under the umbrella of Pervasive Developmental Disorders (PDD), a category of neurological disorders characterized by severe and pervasive impairment in several areas of development, including social interaction and communications skills. The five disorders under PDD include Autistic Disorder, Asperger's Disorder, Childhood Disintegrative Disorder (CDD), Rett's Disorder, and PDD-Not Otherwise Specified (PDD-NOS). Specific diagnostic criteria for each of these disorders can be found in the American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision. Washington, D.C., American Psychiatric Association, 2000, as distributed by the American Psychiatric Association.
There is no definitive diagnostic test for biological manifestations of autism, and thus it remains one of the only neurological disorders that must be diagnosed almost entirely through behavioral symptoms. The DSM-IV classifies autism as a Pervasive Developmental Disorder (PDD) characterized by twelve diagnostic criteria. Those criteria fall into three categories: impairments in social interaction; impairments in communication; and a restricted repertoire of activities and interests. A diagnosis of autism requires that a child display at least six of the twelve symptoms.
If a child does not fit the definition of autism given above, he/she may be diagnosed with a condition called Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS). Such a diagnosis of non-specific forms of Pervasive Developmental Disorder (PDD) may include atypical types of autism that do not fall into the above categories because of late age of onset, for example, or sub-threshold or atypical symptoms. According to the DSM-IV, this diagnosis is to be used when autistic-like behaviors are present, in particular when there is severe impairment in the development of social and verbal communication skills, but the child does not meet the criteria for classic autism or any other specific Pervasive Developmental Disorder, Schizophrenia, Schizotypal Personality Disorder or Avoidant Personality Disorder.
A variety of agents have been postulated to be associated with the development of autism including, but not limited to, exposure to pesticides and/or agents that can cause birth defects. In at least some cases, it appears that autism may have a genetic basis. The genetics of autism appear to be complex. For example, copy number variation and chromosomal structural abnormalities (both large and small) have been shown be present in particular genomic regions in patients with autism or syndromes in which autistic behavior is common (Abrahams and Geschwind, Nature Reviews Genetics, 2008, 9:341-355). DNA hybridization studies have shown structural abnormalities in autistic populations. A causal role for genetic variation in many different genes has been suggested based on evidence from association or linkage studies. Still, genome wide association studies have failed to link specific common variants, acting singly or in combination, though such studies have identified association peaks that may point to other causative genes or pathways. There is some evidence that genetic variation may be the cause of at least non-syndromic autism.
Evaluations to diagnose a child are made by a team typically including doctors and the child's parents. Because diagnosis of autism spectrum disorders is subjective, misdiagnosis of a child can frequently occur. Thus, there is an unmet need for diagnostic tests that can provide an objective determination of whether a subject suffers from an autism spectrum disorder.